Create safe helper for LLVMSetDLLStorageClass

compiler/rustc_codegen_llvm/src/llvm/mod.rs

@@ -403,3 +403,9 @@ pub(crate) fn add_module_flag_str(
         );
     }
 }
+
+pub(crate) fn set_dllimport_storage_class<'ll>(v: &'ll Value) {
+    unsafe {
+        LLVMSetDLLStorageClass(v, DLLStorageClass::DllImport);
+    }
+}